Two strains of Gram negative anaerobic rods isolated from periodontosis patients have been shown to cause severe alveolar destruction as monocontaminants in gnotobiotic rats. The present investigation will attempt to measure the humoral and cellular immune response to the test organism in gnotobiotic rats using in vitro and in vivo measurements. In a second series of experiments, gnotobiotic rats will be sensitized to the test organisms before or after implantation of viable organisms. The effect of sensitization on the immune response, the number of organisms per quadrant and the course of disease will be monitored using mirobiologic, immunologic and histologic techniques. Optimal chemotherapeutic agents will be sought in vitro to control the Capnocytophaga and Y4 organisms. The effect of such agents on the course of disease and microbial colonization will be monitored in gnotobiotic rats monoinfected by the suspected pathogens.